PROJECT SUMMARY The recently discovered intrinsic photosensitive retinal ganglion cells (ipRGCs), which express melanopsin photopigment, are a third class of photoreceptors in mammalian retina other than rods and cones. Research thus far has shown that ipRGCs play a very important role for a number of sub-conscious non-image-forming functions, such as circadian photoentrainment, the pupil light reflex, sleep and mood regulation. Nevertheless, it is unclear whether melanopsin activation in ipRGCs contribute to visual processing. IpRGCs provide feedback to dopaminergic amacrine cells to restructure retinal processing and also send direct signals to the lateral geniculate nucleus (LGN) in the thalamo-cortical visual pathways. Therefore, melanopsin activation in ipRGCs may alter visual processing. However, how melanopsin affects visual processing, particularly in humans, is unclear. The proposed research will use a lab-made device that allows independent control of melanopsin, rod and cone stimulations to investigate how different melanopsin activation levels in ipRGCs affect physiological responses in the visual pathways. We will record flicker and pattern Electroretinogram (ERG) and Visual Evoked Potential (VEP) simultaneously to assess whether melanopsin?s effects are mediated by intraretinal signaling, ipRGC-to-LGN projection or both. The physiological results will be correlated with psychophysical measurements under the same conditions. Our project will help to advance our understanding of the mechanisms for melanopsin activation to affect visual processing.